Field of the Invention
The present invention relates to a wafer processing method for dividing a thin wafer having a functional layer formed on the front side to obtain individual devices.
Description of the Related Art
There is a wafer composed of a substrate such as a sapphire substrate and an SiC substrate and a functional layer formed on the upper surface of the substrate through a buffer layer. The functional layer (called also light emitting layer or epitaxial layer) is composed of an n-type semiconductor layer and a p-type semiconductor layer. The functional layer is partitioned by a plurality of division lines to define a plurality of separate regions where a plurality of light emitting devices are formed on the front side of the wafer. Further, there is a wafer composed of the above-mentioned substrate and a functional layer formed on the upper surface of the substrate through a buffer layer, wherein the functional layer is formed from a GaN semiconductor layer. This functional layer is partitioned by a plurality of division lines to define a plurality of separate regions where a plurality of power devices are formed on the front side of the wafer. In either case, the wafer is cut along the division lines by using a dividing apparatus such as a laser processing apparatus, thereby obtaining the individual light emitting devices or power devices, which are used in various illuminating equipment or electrical equipment such as television set.
Each device mentioned above is used in a mobile phone, wrist watch having a communications function, etc., and it is therefore desirable to develop a technique of further reducing the thickness of each device in order to further reduce the size and weight of each equipment mentioned above. As a technique of reducing the thickness of each device in dividing a wafer into devices, there has already been proposed a technique called dicing before grinding (see Japanese Patent Laid-Open No. 1999-040520, for example).
This technique includes the steps of first forming a groove having a depth corresponding to the finished thickness of each device on the front side of a wafer along each division line, next providing a protective member on the front side of the wafer, and next grinding the back side of the wafer until the groove is exposed to the back side of the wafer, thereby dividing the wafer into the individual devices.